The present invention relates to signal coding.
The coding of a digital signal often includes a step which takes into account the order statistics of the words comprising the signal, the "order statistics" being the order of the frequency of occurrence of those words. Perhaps the most well known of such coding schemes is variable-length coding wherein the frequency with which a particular signal word is expected to occur vis-a-vis the frequency with which the other signal words are expected to occur determines the length of the codeword to which that signal word is assigned; the greater the expected frequency of occurrence, the shorter the codeword.
One approach for carrying out a variable-length or other coding scheme of this type is to explicitly determine the order statistics of the words to be coded before performing the coding itself. Such an approach is advantageous in that the codeword assignment scheme is assured to be optimal for the particular signal being coded. However, a table or "dictionary" setting forth the codeword assignment scheme must be created for each coded signal, thereby, for example, increasing the amount of information to be transmitted and/or stored in order to recreate the signal.
An alternative approach is to generate the codeword set based on an analysis of the order statistics of a representative set of signals in a particular, fairly narrow category, e.g., run-length-coded bilevel images. The variable-length or other code is then created on the basis of that analysis. In this way, the order statistics of the signal actually applied to the coder is likely to be very close to the order statistics with which the coder was designed. At the same time, however, the coder will only efficiently code signals having those order statistics.